There are two major reasons for having this symposium. First, Tohoku Univer sity is the place where ultrasound investigations in Japan originated. Starting from the research studies of Professors H. Nukiyama and Y. Kikuchi of To hoku University, Professor J. Saneyoshi of Tokyo Institute of Technology, and Dr. K. Kato of Osaka University - all graduates of Tohoku University - the results spread to all parts of Japan. More recently we have had acoustic macro scopic studies by researchers like Professor N. Chubachi. As regards tissue char acterization, which was the main theme of the symposium,...